The present invention is directed to passive thermal stabilization of a wavelength monitor, i.e., making the wavelength monitor less sensitive to variations in ambient cavity temperatures, without feeding back this information to the light source being monitored itself. In particular, the present invention is directed to providing a shield and/or a temperature control for a wavelength dependent filter of a wavelength monitor.
In telecommunications, it is often desirable to stabilize light emitting devices against drift in emission wavelength. These drifts can occur due to current fluctuations, age, and temperature. The current supplied to the light emitting devices can be controlled using wavelength lockers, including wavelength dependent elements such as a Fabry-Perot etalon, to determine an output wavelength. However, typically these wavelength dependent elements are also sensitive to thermal variations. Thus, unless the temperature of the wavelength dependent element is controlled, the characteristics of the wavelength locker vary significantly in accordance with the temperature and the wavelength cannot be adequately stabilized.
Current solutions to controlling the temperature in wavelength lockers include active thermal compensation and material index compensation. Active thermal compensation typically involves detecting the temperature and using the detected temperature to control the wavelength or to adjust the temperature of the light emitting device itself using a heater/cooler. This solution requires more active elements and increased processing. Material index compensation typically involves using optical elements fabricated of different materials having equal and opposite index-temperature coefficients or of materials having little or no net change in index-temperature coefficient. However, these materials are wavelength dependent, so they are not reliable over a large wavelength range.
The present invention is therefore directed to a passive thermal stabilization of a wavelength monitor which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
It is an object of the present invention to minimize the effect of ambient cavity temperatures on the wavelength monitor. It is a further object of the present invention to effectively control the temperature of the wavelength monitor.
At least one of the above and other objects may be realized by providing an optical sub-assembly for use with a wavelength monitor including a submount on which two detectors are to be provided, a wavelength dependent filter mounted adjacent to one of the two detectors, and a shield portion extending from the submount over the wavelength dependent filter.
The submount and the shield portion extending therefrom may a single piece. The shield portion may extend over at least two surfaces of the wavelength dependent interference filter. The wavelength dependent filter may be an etalon. The optical sub-assembly may include a substrate on which the submount is mounted. The wavelength dependent filter may be mounted on the substrate. The shield portion may extend in an optical path of a detector, the shield portion having a hole in the optical path of the detector. The shield portion may be coextensive with an edge of the submount. The optical sub-assembly may include electrical interconnection tracks for the detectors, the electrical interconnection tracks extending along the shield portion.
The optical sub-assembly may include a mimicking element having thermal characteristics matched to that of the wavelength dependent filter. A temperature detector may be on the mimicking element. A thermal adjuster adjusting the temperature of the wavelength dependent filter controlled by the temperature detector may be included. The wavelength dependent filter may be mounted directly on the thermal adjuster. The optical sub-assembly may include a substrate, with the wavelength dependent filter is mounted on one side of the substrate and the thermal adjuster mounted on an opposite side of the substrate.
The optical sub-assembly may include a temperature detector mounted on one of the submount and the shield portion. A thermal adjuster adjusting the temperature of the wavelength dependent filter controlled by the temperature detector may be included. The temperature detector may be mounted on a section of one of the submount and the shield portion that most closely matches the thermal response of the wavelength dependent filter.
At least one of the above and other objects may be realized by providing an optical sub-assembly for use with a wavelength monitor including a wavelength dependent filter, a mimicking element having thermal characteristics matched to that of the wavelength dependent interference filter and subject to similar thermal conditions as the wavelength dependent filter, a temperature detector on the mimicking element, and a thermal adjuster controlled by the temperature detector, the thermal adjuster adjusting a temperature of the wavelength dependent filter.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.